The subject matter disclosed herein relates to planar transformers and busbars and, more particularly, to a planar transformer and busbar integrated together as a single component for use, for example, in relatively high power electrical distribution and power conversion device applications.
A planar transformer and a planar inductor each typically comprises a plurality of parallel and/or interleaved copper conductors, separated by insulation layers, arranged in a stack and surrounded by a core. The planar transformer has oftentimes two separate strings of one or more serial connected coils, one string being the primary circuit and the other string being the secondary circuit, with the coils of each circuit commonly being interleaved with one another. Insulation layers may be interleaved with each coil of the primary circuit and the secondary circuit. A planar inductor has oftentimes only one string of one or more serial connected coils. These devices are used in applications such as relatively low power DC-DC converters and power conversion devices, and to a lesser extent in high power applications. Planar transformers and inductors are relatively compact in size compared to the common wound versions, and these planar devices may be designed with relatively higher efficiency and increased thermal management.
Planar transformers can be made with traditional laminated printed circuit board (“PCB”) technology, and may even be embedded within the PCB itself. However, in the power range of 1.5 kW or greater, or when electrical currents exceed 100 A, the ability to use traditional PCB technology for planar transformers is at its limits or is exceeded. Relatively high currents require relatively thick copper conductors (e.g., 0.2 mm up to 0.8 mm or greater), which is beyond the capability of typical PCB manufacturing processes. One of the problematic PCB manufacturing processes is the etching process, in which the edges of the circuit become increasingly less defined (i.e., “fuzzy”) with increasing copper thickness. Also, processing time increases significantly with increasing thickness of the copper layer. An alternative process, such as electrolytic copper plating to increase the copper thickness, is relatively expensive and the planarity of the conductor surface becomes more problematic as the thickness increases.
On the other hand, laminated busbars are suitable for circuits that conduct high frequency alternating currents. A busbar typically comprises a stack of a plurality of parallel and/or interleaved copper conductors, separated by insulation layers. The relatively high currents utilized in busbars require conductors with a relatively thick copper gauge to reduce resistance and excessive heating. Instead of chemical etching, the preferred methods to form the conductor paths are mechanical processes such as, for example, punching, water jetting, laser cutting, milling, and others.
The busbar circuit may have flat conductors that are positioned parallel to each other, with a relatively small distance in between different layers and the conductor layers are separated by layers of insulating material to form a stack. The insulation material, with or without an adhesive coating applied in advance or during the process, is typically positioned between the conductors and all the layers in the stack are pressed together in a lamination process using heat and pressure, resulting in a solid busbar circuit. Due to the relatively good thermal conductivity of copper, the busbar also has a relatively good thermal spreading capability. The exposed surface of the busbar also makes it relatively easy to cool.
Relatively high power DC-DC converters are finding increased use where power storage devices (e.g., batteries, super capacitors, etc.) are used. Other typical high power DC-DC converter applications include hybrid electrical vehicles, military, avionics, windmill pitch control and emerging applications related to renewable energy sources that produce DC voltage (e.g., solar).
It is known that when a busbar is used in a relatively high-power DC-DC converter (typical greater than 1.5 kW), the planar transformer, and most often the inductor, are separate components. The planar transformer, busbar and inductor are typically within the AC portion of the DC-DC converter. Other applications can be in the rectifier. The secondary circuit of the transformer is typically mounted to the busbar by means of screws and bolts, and drums if needed, or by soldering or other connection methods. The typically single interconnection location between the planar transformer and the busbar can be ground for additional connection losses, thereby creating an undesirable hot spot or local heating at that single connection location due to all of the electrical current being concentrated to one side at the single connection location.
As the power density increases, the temperature in the planar transformer tends to increase, as a result of which passive or active cooling may be required. Conductive, convection, or liquid cooling of the planar device is typically carried out through the ferrite core (or other suitable core material), in which the core is connected to a cooling plate, heat spreader or other cooling device or system.
What is needed is a planar transformer and a busbar integrated together to form a single integral component for use in relatively high power electrical distribution and conversion device applications, wherein integrating the planar transformer with the busbar creates a relatively more balanced connection between the transformer and the busbar, thereby improving the flow of current between the transformer and the busbar and reducing interconnection losses and electrical current hotspots.